Objective:
Objective 1: Identify psychological and physiological processes and factors that influence the motivation to exercise and to eat.
Objective 1A. Determine whether incentive sensitization for physical activity is dependent on the dose and the pattern/intensity of physical activity.
Objective 1B. Determine whether the level of negative energy balance influences the magnitude of alterations in food reinforcement.
Objective 2: Determine whether the relative reinforcing value of vegetables or fruits can be increased through repeated exposure.
Objective 3: Develop a tool based on breath carbon stable isotope ratio to provide biofeedback regarding energy balance and to promote healthy weight choices.
Objective 3a: Determine if overconsumption of calories will increase breath d 13C when subjects are in negative energy balance
Objective 3b: Determine the threshold at which dietary 13C intake causes a detectable increase in breath d 13C in subjects in negative energy balance.
Objective 3c: Determine if biofeedback based on breath d 13C will result in reduced food intake of individuals trying to maintain negative caloric balance.

Approach:
Achieving and maintaining healthy body weight underlies many critical aspects of health. The immediate choices people make about their foods and physical activities have cumulative effects that affect body weight and, ultimately, health. Yet, the motivational bases of those choices remain poorly understood; as are ways those choices may be moved towards healthier alternatives. This knowledge is needed for the development of new and effective tools to promote behavioral choices that support healthy body weight. This project addresses these needs by investigating how to increase the reinforcing value of physical activity, and ways to increase the reinforcing value of vegetables and fruits. It also will evaluate the motivating potential of providing real-time feedback on subject energy balance based on an analysis of breath. This project will yield empirical evidence that will inform dietary and physical activity guidelines and programs, and tools that can be used by workers in the health and fitness industries to help individuals make healthy choices regarding physical activity, diet, and maintenance of a healthy body weight.